Swim fin



NOV. 19, 1968 N, MURDQCH 3,411,165

SWIM FIN Filed Dec. 12, 1966 745m) 5 Jaw/7 A rive/v57 United States Patent Oifice 3,41 1,165 Patented Nov. 19, 1968 3,411,165 SWIM FIN Frank N. Murdoch, Bellevue, Wash. (527 Summit, E 302, Seattle, Wash. 98102) Filed Dec. 12, 1966, Ser. No. 601,233 3 Claims. (Cl. 9-309) ABSTRACT OF THE DISCLOSURE This invention is concerned with a swim fin having a relatively thin, transversely bowed, nonstretched, bellied web which reversibly cups during swimming by reason of marginal portions flexibly being secured to the front of a shoe-like member and to the inner portions of diverging substantially inflexible forward extending ribs.

Background Swim fins have been used for a considerable period of time for the purpose of making the human much more effective in swimming through the water. Their value is highly appreciated and there have been numerous forms of devices brought forth to aid the swimmer. In most such devices means is provided comprising a recess into which the swimmers foot is inserted. Customarily this foot encasing member generally extends over the metatarsal area of the foot. Normally a strap between opposite sides of the foot encasing member passes around the heel to secure the swim fin in place on the foot. Ahead of the foot encasing member is usually a splayed flipper or blade which is caused to flutter in the water as the swimmer raises and lowers his foot in the manner customary to swimming.

Ordinarily swim fins have been made so that the blade is flexible and bends or pivots about an axis generally transverse of the front portion of the swimmers foot. Thus as the swimmer is raising his foot in the up cycle in the water the tip of the blade arcs downward relative the heel and varying degrees of bend are obtained as the leg moves through an arc. This results in a certain amount of horizontal thrust, greater than that normally obtained by a swimmer without a fin, thus producing more advantageous forward movement. During the down cycle of the leg, the flexible tip of the fin reverses its arcuate disposition and to a lesser degree another increment of horizontal forward thrust is obtained. The flexure of the swim fins in both directions of motion are rather well disclosed in the Churchill Reissue Patent Re 23,006.

The prior swim fins have generally been formed of molded rubber having a suitable hardness to impart durability, but having softness and being highly flexible and resilient.

Description of the invention This invention is best described by reference to the accompanying drawings in which:

FIGURE 1 is a perspective view of a swim fin in accordance with this invention;

FIGURES 2 and 3 are schematic Side views of a swim fin respectively showing its action during the down and an up stroke;

FIGURES 4, and 6 are a series of cross-sectional views taken on lines 4-4, -5--5, and 66 respectively of FIGURE 1;

FIGURES 7, 8 and 9 are enlarged cross-section taken in planes substantially the same as in FIGURES 4, 5 and 6 respectively of a side reinforcing rib incorporated in the swim fin; and

FIGURE 10 is a longitudinal sectional view.

The swim fin 10 comprises a shoe-like member 12 shaped to receive and encase the forward portion of a swimmers foot. It has a sole 14 underneath and, at the rear, a strap 16 extending between the sides of the foot encasing portion 12, and passing behind the swimmers heel. Ordinarily the shoe-like portion 12 covers the metatarsal portion of the foot and extends into fairly close proximity to the ankle.

The foot portion 12 is semirigid, being formed of rubber of suitable durometer hardness to give it substantial strength and form. It is desirable that it not be appreciably flexible although resilience and surface softness is desirable.

Ribs 18, 18 extend forward in a diverging manner from the opposite sides of foot portion 12. Ribs 18 should be substantially inflexible in vertical planes. Internally the ribs 18, 18 may each contain elongated relatively rigid stiffener 20 to reduce flexibility in the desired manner. On some occasions a single pair of ribs 18, 18 may be used. It appears preferable that a medial rib 22 be located between ribs 18, 18 to extend forward from the shoe-like portion 12 and to divide the space between ribs 18, 18. Obviously more than a single intermediate rib 22 may also be provided between the ribs 18, 18 within the spirit of this invention.

Between medial rib 22 and each of the adjacent side ribs 18 is a web 24 formed of thin flexible sheet material of rubberlike nature. The webs 24 are not stretched and are baggy, having a tendency to belly in the at-rest position as shown in FIGURE 1. Marginal portions of the bellied webs are flexibly secured at their sides to the ribs 18 and 22. At the rear of the webs they are secured to the foot encasing portion 12 of the swim fin. The thinness of the sheet material forming the webs is such that they tend to transversely bow or belly as shown in the cross-sectional views of FIGURES 4, 5 and 6. They bow either downward, as may be seen in solid lines, or bow upward as is indicated by the dotted lines. The transverse bowing of the webs progressively increases as they extend forward from the shoe-like member. For example, where the concavity of FIGURE 4 is relatively slight, a noticeable increased concavity will be seen in FIGURE 5; likewise note the increase in bowing or belly concavity to be seen in FIGURE 6.

The ribs 18 and 22 have substantial vertical thickness at the point of juncture with the shoe-like member 12. In other words, at its rear a rib 18 has a vertical height that is considerably more than, say, halfway between the shoe-like member 12 and the outer end. This can be seen in FIGURE 8. Near the outer end the rib is more circular in cross-section, the same being shown in FIGURE 9. The inclusion therein of the stiffener, which may be a wire or rod suitably molded in place, is to eliminate or reduce the tendency of the ribs to arc or bend in the flaring action of prior swim fins. To put it another way, it is desirable to have as stiff a rib as possible.

By reason of the flexible joinders 25 between webs 24 and their marginal ribs, the webs bow to one side of the ribs during a down stroke of the swimmers leg as may be seen in FIGURE 2. Then they reverse themselves and bow to the opposite side of the ribs on the upstroke as may be seen in FIGURE 3. The result is that tapered, cup-shaped pockets between the ribs work upon the water. Movement tends to expel water rearward from the pockets, thereby developing a forward or horizontal thrust effective to move the swimmer through the water.

It has been observed with swim fins according to this invention that there is substantially equal thrust forward on the down stroke as well as on the upstroke. This differs from analyses of flexible blade fins wherein the forward thrust on the down stroke is in the order of 35 to 25% of the thrust on the upstroke. While the cupping of the webs first to one side and then to the other side may superficially appear to afford a tip action in the fins that is similar to the flexible legs of the older swim fins, it is believed that the cupping of the web in some unknown manner gives the swimmer a more effective purchase upon the water. Without excessive exertion he can propel himself through the water with greater speed and agility than previously.

The cross-sections of the webs 24 is desirably uniform throughout up to their points of marginal joinder with the ribs 18, 18 and 22 and the foot-like member 12.

Desirably this structure is molded as a unit. Or the shoe-like portion 12, the ribs 18, 18, 22 and the heel strap may be molded as a unit and the webs 24, having been previously formed or cut from sheet stock are marginally secured by rubber adhesion techniques in place between the ribs and to the shoe-like portion.

What is claimed is:

1. A swim fin, comprising:

a semirigid shoe-like member to receive and encase the foot and including means to pass around the heels;

a substantially inflexible rib extending immovably forward of said shoe-like member at each side thereof, said ribs forwardly tapering and diverging relative to each other;

between said ribs a thin web having margins flexibly secured to the front of the shoe-like member and at the sides to said ribs; and

said web having a uniform thickness throughout and being wider than the space between said ribs whereby the web may belly oppositely between said ribs during swimming.

2. A swim fin as in claim 1 in which the shoe-like member and the ribs are integrally formed of rubbery material an each rib contains an elongated, relatively rigid stiffener means operable to impart inflexibility thereto.

3. A swim fin as in claim 1 in which there is a medial rib disposed between said side ribs and extending forward of said shoe-like member, and a thin bellied Web is disposed between each side rib and said medial rib.

References Cited UNITED STATES PATENTS 1,607,857 11/1926 F. Zukal 9-304 X 3,019,458 2/1962 E. De Barbieri et al. 9-309 3,042,943 7/ 1962 G. Katehis 9309 X FOREIGN PATENTS 1,259,744 3/ 1961 France.

1,278,740 11/ 1961 France.

1,296,314 5/1962 France.

1,078,913 3/ 1960 Germany.

511,942 1/ 1955 Italy.

MILTON BUCHLER, Primary Examiner.

J. P-I'ITENGER, Assistant Examiner. 

